Enable the definition of date format for dates in the dashboard widget

The current value is hardcoded for example at https://github.com/openmrs/openmrs-module-coreapps/blob/master/omod/src/main/webapp/resources/scripts/fragments/dashboardwidgets/visitbyencountertype/visitbyencountertype.html#L3

The default value shall be set to uiframework.formatter.dateFormat global property, however the user can override this value as a configuration option for the widget